Question: The grades on a chemistry midterm at Oak are normally distributed with $\mu = 66$ and $\sigma = 5.5$. Omar earned a $55$ on the exam. Find the z-score for Omar's exam grade. Round to two decimal places.
Explanation: A z-score is defined as the number of standard deviations a specific point is away from the mean We can calculate the z-score for Omar's exam grade by subtracting the mean $(\mu)$ from his grade and then dividing by the standard deviation $(\sigma)$ $ { z = \dfrac{x - {\mu}}{{\sigma}}} $ $ { z = \dfrac{55 - {66}}{{5.5}}} $ ${ z \approx -2.00}$ The z-score is $-2.00$. In other words, Omar's score was $2.00$ standard deviations below the mean.